WO2010111920A1 - Table tennis ball with seamless whole structure - Google Patents

Abstract

A table tennis ball includes a hollow and sealed spherical shell (1) formed in one piece, and is provided with a continuous interior surface (3). The spherical shell (1) is a seamless whole and provided with a substantively uniform thickness of wall. The method for manufacturing the table tennis ball is formed in one piece by rotational moulding.

Description

 a seamless structure of table tennis

Technical field

 The invention relates to a table tennis ball which is seamless overall and has a substantially uniform wall thickness, and the entire inner surface of the table tennis ball is a complete and continuous spherical surface; the invention also relates to a method for manufacturing the table tennis ball. Background technique

 Whether it is a large-scale competition or daily entertainment, the structure of the table tennis used is usually a hollow sealed sphere which is connected by two semi-spherical thin-walled plastic spherical shells by bonding, splicing or pressing. The outer surface of the ball is polished to achieve the requirement of a tight seam, that is, the outer surface of the ball has no visible joints to form a complete continuous spherical surface. The ball of this structure is called a tight seam table tennis. Strictly speaking, the ball is still stitched. Although finely machined, there are still visible joints on the inner surface of the table tennis. Due to the existence of the joint seam, the inner surface of the ball is not a complete continuous spherical surface. At the same time, although the joint of the two hemispherical spherical shells of the ball is a tight joint structure, even if the seam is not visible to the naked eye, There are substantial rework joints present. In terms of materials, celluloid remains the main raw material for table tennis. At present, the game ball approved by the ITTF, in order to meet the performance requirements, its material is still celluloid. Although celluloid materials have well-known instability and flammability, they are prone to fire safety accidents during production, and the process of making table tennis with celluloid is complicated, the production cycle is long, and the cost is high. The performance index is high, and it is limited by the production process. Choosing other materials instead of celluloid to make table tennis is not a practical application condition. To this end, the ITTF clearly defines in its Technical Leaflet T3 standard (hereinafter referred to as the Τ3 standard): Encourage and support manufacturers to develop new and better materials to replace celluloid, in order to produce better and more stable performance. More environmentally friendly table tennis.

In the Τ3 standard, the ITTF has strict regulations on the diameter (also called roundness), weight, eccentricity (also called rolling), hardness, and bounce of table tennis. Therefore, to make new Table tennis made by materials or new molding processes can replace the current celluloid table tennis. It is quite difficult to achieve similar or exceed the requirements of several standards such as eccentricity (also called rolling), hardness, and bounce. . Over the years, some units or individuals have been studying this aspect. For example, in the new table tennis molding process, a method of manufacturing table tennis by extruding a plastic and then similarly blowing a mold into a mold is disclosed in Chinese Patent Application No. 01126885. The table tennis produced is difficult to achieve uniform wall thickness, so the T3 standard is not met in both the hardness requirement and the bounce requirement. In the development of new table tennis materials, Chinese Patent Application No. 90103206. Modified polystyrene-based material, Chinese application 200680034220. X also discloses an organic non-crosslinked polymer for replacing celluloid, and a process for processing table tennis using the synthetic material; domestic Pisces Brand table tennis manufacturers such as Red Double Happiness have also carried out related research in this respect, but these new materials are still using the molding process similar to traditional table tennis in the molding process of making table tennis, that is, using injection molding or stamping. A plurality of shell pieces or hemispherical shells are formed, and then a plurality of shell sheets or two hemispherical shells are joined by bonding, splicing, pressing, or the like to form a hollow sphere. Although these techniques have changed the material of table tennis, the production process is still as complicated as traditional table tennis. Even if the manufactured table tennis meets the requirements of the T3 standard, the production cost is difficult to reduce.

For the most widely used process for manufacturing table tennis, it can be summarized that two hemispherical spherical shells are first produced, and then the two hemispherical spherical shells are later bonded to form a sealed hollow table tennis ball. In production, it is necessary to ensure the uniform thickness of the two hemispheres, and to ensure the weight accuracy of the ball, and to ensure reliable bonding. The common features are many processes, complicated processes, difficult production, and low product qualification rate. With this post-bonding production process, from the outer surface of the ball, the bonding joint is polished after the expansion of the ball to meet the requirements of the tight seam. The outer surface of the ball can be considered as a complete and continuous spherical surface. However, the inside of the ball obviously protrudes from the inner surface of the ball at the joint seam, forming an annular convex strip. Therefore, the wall thickness of the spherical shell at the joint and the wall thickness at other positions are obviously different. The ball formed by the blow molding process has a clearly visible concave band on the inner surface of the ball at the press-fit joint, so the wall thickness and other positions at the seam are also different. Looking at the inner surface, it can be clearly seen that the table tennis is also made up of two hemispherical shells. Regardless of the process, the presence of raised or depressed strips makes it difficult to match the hardness of the seams to the hardness of the top and other locations of the hemispheres. The elastic (bounce) in use is also difficult to match. The inner surface is also divided into two parts by a raised strip or a recessed strip, which is not a complete continuous spherical surface, which increases the elastic control requirements and difficulty of the ball, and also reduces the life of the ball. Under the current technical conditions, the inner surface of the ball is not a convex band on the inner surface when the two hemispherical shells are bonded, so that the inner surface of the ball is a complete continuous spherical surface as the outer surface, which cannot be achieved by the process, even The adhesion fastness at the seam is also difficult to guarantee. At the same time, although the naked eye is not visible, there will still be reworked seams in the shell of the spherical shell, and the service life of the ball will be reduced. Even if the two hemispheres are connected by splicing, pressing, etc., there will be similar problems as described above. Therefore, as long as there is a joint seam, even if it does not protrude or dent on the inner surface of the ball, it will affect the quality of the ball. Therefore, if you do not change the existing existence of the existing table tennis, the structural defects of the joint seam and the wall thickness are inconsistent. Even if the quality competition is more stable and environmentally friendly, it is difficult to produce quality and performance than the current game. A product that has changed significantly from table tennis. Summary of the invention

 In order to overcome the deficiencies of the prior art, the present invention provides a table tennis ball having an overall seamless structure and improved performance. The table tennis ball is formed by a rotational molding process, and the inner and outer surfaces of the spherical shell are continuous spherical surfaces, Any visible joint, gp, shell of the spherical shell does not have any rework joints in the form of joints, creases, seams, etc., and the shell has a uniform uniform wall thickness, which is more conducive to Various technical indicators of table tennis.

 The invention also provides a method for manufacturing the above-mentioned table tennis, which adopts a rotational molding process to form a hollow spherical shell of a suitable wall thickness in a cavity, thereby producing a new type of table tennis ball having continuous inner and outer surfaces without joint seams, and The production process is simple and easy to control, which is conducive to industrial scale production. While producing high quality table tennis, it also reduces the production cost.

First of all, the present invention provides a table tennis ball different from the existing products, the table tennis is once The molded hollow sealed spherical shell has a continuous inner surface.

 The more prominent feature of the table tennis provided by the present invention is that the spherical shell is seamless overall, and the inner and outer surfaces of the spherical shell have no reworked joint seams.

 Preferably, the table tennis of the present invention is produced by a rotational molding process.

 According to the solution of the present invention, the spherical shell of the table tennis ball is filled with gas, and the pressure is less than 9 standard atmospheric pressures, so that the ball hardness and bounce standard are better met; preferably, the pressure of the inflatable body in the spherical shell does not exceed 3 standard atmospheres.

 The ping-pong ball of the present invention has no reworked joint seam, the spherical shell has a substantially uniform wall thickness, and the wall thickness of the spherical shell is less than ±0.04 mm (the absolute value of the wall thickness difference is 0.04 mm)

 The table tennis material of the present invention may be selected from materials such as polyolefin, nylon, polycarbonate, polyester, ABS or PS which are advantageous for the rotational molding, thereby contributing to the improvement of safety in production.

 The invention also provides a method for preparing the above table tennis, the method comprising the steps of: adding raw materials for making table tennis into a spherical mold conforming to the size of a table tennis ball and closing the mold, and setting the spherical mold to rotomold molding In the apparatus, the axes of the two rotating shafts of the rotational molding device are passed through the center of the spherical cavity of the mold, and the axes of the two rotating shafts are perpendicular to each other; the spherical mold is simultaneously rotated around the two rotating shafts And control the speed range from 20 rpm to 3000 rpm, so that the raw material that can flow in the mold is uniformly attached to the inner wall of the cavity of the mold under the centrifugal force and its own gravity, and the raw material is solidified into a spherical shell; Release the ball shell.

 The manufacturing method of the present invention further comprises subjecting the demolded spherical shell to a surface treatment to obtain a table tennis product having an outer surface meeting the standard.

 The "flowable raw material formed in the mold" described in the above method for producing table tennis includes a molten material, a liquid state or a paste-like flowable material formed by heating the mold or chemical reaction between materials, and a specific forming manner and The flow dynamic form depends on the choice of material.

 In order to adjust the jumping force of the table tennis ball, after the mold is closed, the mold can be selectively filled with a certain pressure of gas so that the demolded spherical shell has a pressure of no more than 3 standard atmospheric pressures.

In summary, the table tennis provided by the present invention is composed of only one sealed ball shell formed at one time. The wall thickness of the spherical shell is basically the same, the whole is seamless, gp, the shell of the spherical shell does not have any reworked joint seams in the form of bonding seams, crepe seams, nip seams, etc., and the entire interior of the table tennis, The outer surface is a complete continuous sphere. This new structure of table tennis, uniform bounce, and good overall performance.

 The table tennis provided by the invention only needs to be selected from the well-known materials suitable for the existing rotational molding process, such as polyolefin, nylon, polycarbonate, polyester, ABS and PS, and the material is stable and environmentally friendly. The material, once formed by the rotational molding process, can produce table tennis products with higher requirements than the ITTF T3 standard in eccentricity, hardness and bounce. The ping-pong table made by the invention has the advantages of simple molding process and convenient operation. At the same time, the related equipment of the rotomolding molding has the advantages of simple structure, small volume, low power consumption, low product cost, no pollution to the environment during the production process, and is favorable for table tennis. Mass production.

 The specific technical solution that can be adopted by the present invention is: selecting a cavity of the molding die to be spherical, so that the mold simultaneously rotates at a high speed in two axial directions perpendicular to each other, and the two rotation axes of the rotational molding device pass through the spherical cavity The center of the ball controls the internal material of the mold to become the flow dynamic while rotating. Under the combined action of the centrifugal force and the gravity of the material itself, the liquid, molten or paste-like material in the cavity can be evenly rotated during the rotation. Distributed on the inner wall of the spherical cavity to maintain the normal rotation of the mold, the material coated on the inner wall of the cavity solidifies into a solid, and after demolding, a hollow sphere is obtained, and then the outer surface is polished and then processed. Get a table tennis ball that is seamless overall and has the same wall thickness. The table tennis ball is composed only of a complete hollow sealed thin-walled spherical shell. The spherical shell is a one-piece integrated structure, and the whole is seamless. The shell of the spherical shell does not have any joints such as joints, crevices, and seams. The reworked joint seam of the same form, the spherical shell has the same wall thickness at any position, the inner surface of the spherical shell has no visible joint seam, and the entire inner and outer surfaces of the spherical shell are a complete continuous spherical surface (now The table tennis made by the craft is only polished by the later process, and only the outer surface is basically a continuous spherical surface).

In the embodiment of the present invention, after discharging into the mold cavity and closing the mold, it is preferable to further fill the cavity with a certain pressure of gas, and to ensure a fully sealed closed mold, gP, in the condition of no leakage and no leakage. Under After re-rotation molding, the formed table tennis ball has the same gas pressure inside the hollow interior of the spherical shell as the gas filled in the cavity before molding. In this way, in the case of producing table tennis with the same material as compared with the prior art, the present invention can adjust the performance of the bounce and hardness of the table tennis in a certain range, and make the bounce more stable. When the user plays table tennis, the ball feels better and the front of the ball is stronger. Normally, the pressure of the gas inside the table tennis is below 9 standard atmospheres. If the air pressure is too high, the table tennis will be easily deformed and the ball may be broken. The present invention preferably controls the internal pressure of the table tennis to be below 3 standard atmospheres.

The table tennis ball provided by the invention with the same seamlessness and substantially the same wall thickness utilizes the well-known rotomolding (also called spin molding, rotary molding, rotary molding, rotary casting, rotary forming, etc.) process, and On this basis, a simple change is made to rotate the mold at the same time around two mutually perpendicular and through the axis of rotation of the mold core. The material in the cavity is uniformly attached to the inner wall of the mold cavity under the action of centrifugal force and its own gravity. (The invention is also referred to as a biaxial centrifugal force rotational molding process). The existing rotomolding process is an important method for producing large and extra large hollow plastic products. If it is used to produce small products such as table tennis, even if it meets the requirements of relevant standards, its production efficiency is very low, resulting in higher production costs. On the other hand, in the production of rotational molding, although the mold can rotate around two axes (vertical and horizontal axes) perpendicular to each other at the same time, the usually processed rotomoulded products are large-sized products of different shapes, in order to make the cavity The material can flow and be applied to various positions on the inner wall of the cavity, and the control mold speed can not be high, usually within 20 rev / min. If the rotation speed is too high, the local position will not be coated or uneven, and the produced product is waste. When the mold rotates at a low speed, the liquid, molten or pasty material is applied layer by layer on the inner wall of the mold cavity by its own gravity. Due to the two-layer coating and low rotation speed, the molding is performed. The thickness of the wall thickness of the product is usually 0. 20 mm 1. 20 mm (for large size) Products, such perfectly acceptable variation in wall thickness). The average thickness of the spherical shell of the existing celluloid table tennis is less than 0. 55 mm, and the relevant standard has a high requirement for the accuracy of the wall thickness. In the eccentricity test, it is difficult to meet the requirements of the T3 standard, and the wall thickness error will also result in different positions of the table tennis ball shell. The hardness is not uniform, the bounce is uneven, and it is difficult to meet the requirements of the T3 standard in terms of hardness and bounce. According to the method of the present invention, a hollow spherical article having a smaller diameter including a table tennis ball is produced. Generally, when the spherical article has a diameter of 120 mm or less, the processing is very economical, and the existing plastics which can be used for the rotational molding process, such as polyolefin. Nylon, polycarbonate, polyester, ABS, PS, etc., can be obtained by the biaxial centrifugal force rotational molding process of the present invention to obtain a hollow spherical product having uniform wall thickness. The basic production steps of the charging, heating, rotary forming, cooling, demoulding, and mold cleaning of the manufacturing process of the present invention are exactly the same as the existing rotational molding process, and the production is adjusted according to the fluidity of the processed materials. With the rotation speed of the two rotating shafts, it is possible to stably produce a table tennis or other hollow spherical product which is seamless and has the same wall thickness. In the process of the present invention, since the material is directly attached to the inner wall of the cavity quickly by the combination of centrifugal force and gravity, instead of slowly coating layer by layer as in the existing rotational molding process, the product quality is shortened while ensuring product quality. In the production cycle of the product, an average production cycle from loading to demolding is saved by an average of one-third of the time, which means that the manufacturing process provided by the present invention can produce high-quality table tennis while producing efficiency. Higher, lower cost. The results of the test and the mass production test show that the wall thickness error of the spherical shell of the table tennis ball provided by the present invention can be accurately controlled within 0.04 mm, even lower than 0.03 mm, therefore, relatively traditionally by two hemispheres In the case of a combined table tennis ball having a significantly different wall thickness, it can be said that the spherical shell of the overall seamless table tennis ball has the same wall thickness at any position. The other test indicators include: eccentricity test results, the table tennis off-center line range is 0-156 mm (T3 standard is 0_175 mm) _; for the hardness of the ball, the table tennis hardness range is 0. 72mm-0. 79mm (T3 The standard is 0. 71mm_0. 84mm); the ball's bounce force test, the table tennis bounce range is 248mm-260mm (T3 standard is 240mm-260mm); therefore, the new type of table tennis provided by the present invention completely reaches the quality of T3 Standard requirements.

The utility model has the beneficial effects that the table tennis ball is composed of only one sealed spherical shell which is formed at one time, the wall thickness of the spherical shell is the same, and there is no reworked joint seam in the shell of the spherical shell, and the inner surface of the spherical shell is also There are no visible joints of any kind. In the implementation of the solution of the present invention, it is only necessary to select materials with stable materials and environmental protection in the well-known plastics suitable for the existing rotational molding process, and a large number of materials can be obtained. The production of table tennis with good performance and environmental protection. Tested in the production process, the table tennis provided by the invention achieves higher requirements than the T3 standard in several aspects such as eccentricity, hardness and bounce. Since the table tennis is integrally formed at one time, the process is small, the process is simple, the product qualification rate is high, and the cost is low, and the cost of the ball is only 60%-72% of the existing celluloid table tennis. The production equipment has low input cost, small land occupation, low energy consumption, and no pollution to the environment during production, which is conducive to mass production of table tennis. The term "reworked joint seam" as used in the present invention means that in the production of a sphere, the incomplete spherical shell which has been previously formed is processed into a complete sphere by means of further means such as bonding, splicing or pressing, etc. A joint formed by the surface. DRAWINGS

 1 is a schematic cross-sectional view of a once-formed seamless table tennis ball provided by the present invention.

 Reference numerals in the figure: 1. spherical shell; 2. outer surface; 3. inner surface. detailed description

 The invention will now be further described with reference to the drawings and embodiments.

 In Fig. 1, the spherical shell 1 is a hollow sealed thin-walled spherical shell which is rotated at a high speed and formed at one time, and the inside of the hollow spherical shell is filled with a certain pressure of gas (gas is not shown), and the pressure of the gas does not exceed 3 At a standard atmospheric pressure, the spherical shell 1 has an outer surface 2 and an inner surface 3, forming a complete seamless table tennis. As shown in Fig. 1, since the spherical shell 1 is integrally formed at one time by the rotational molding process, the spherical shell 1 is a seamless and independent structure as a whole, gp, and there is no joint seam, joint, or pressure on the casing. The reworked joints in the form of joints, etc., at the same time, the spherical shell 1 has the same wall thickness (with a wall thickness error of 0.03 mm). The entire surface of the inner surface 3 also has no visible joints of any form and becomes a complete continuous spherical surface. The outer surface 2 is a complete continuous spherical surface that is ground to a T3 standard after molding.

The production process of the table tennis: adding the raw materials for making table tennis into the spherical mold corresponding to the size of the table tennis and closing the mold, and setting the spherical mold in the rotational molding device to make the rotomolding into The two rotating shafts of the type device are perpendicular to each other, and both axes pass through the center of the spherical cavity of the mold; the spherical mold is heated according to the specific conditions of the material or the raw material is chemically changed to become flowable dynamic, so that the spherical mold Simultaneously rotating around the two rotating shafts, and controlling the speed range from 20 rpm to 3000 rpm (the specific speed can be determined according to the properties of the selected material, so that the material can be uniformly attached to the inner wall as the control standard) The flowable raw material in the mold is uniformly attached to the inner wall of the cavity of the mold under the centrifugal force and its own gravity to become the spherical shell 1; after the wall thickness of the spherical shell meets the requirement, the spherical mold is maintained in a rotating state, and the raw material is maintained. Curing becomes a spherical shell, the mold is opened, and the spherical shell 1 is taken out.

 As an alternative solution, after discharging into the mold cavity and closing the mold, it is preferable to fill the cavity with a certain pressure of gas (not more than 3 standard atmospheric pressures), and to ensure a fully sealed closed mold, gp, without leaking The material is ventilated under the condition of no air leakage, so that the formed table tennis ball has the same gas pressure inside the hollow interior of the spherical shell as the gas filled in the cavity before molding. The inflated ping pong ball has superior elasticity.

Claims

Claim  A table tennis characterized in that the table tennis ball is a one-piece hollow sealed spherical shell and has a continuous inner surface.  2. Table tennis according to claim 1, characterized in that the spherical shell of the table tennis is seamless overall.  3. Table tennis according to claim 2, characterized in that the shell of the table tennis ball shell does not have any reworked joint seams, and the inner surface of the ball shell has no visible joint seam.  The table tennis according to any one of claims 1 to 3, wherein the table tennis is produced by a rotational molding process.  The table tennis according to any one of claims 1 to 4, characterized in that the spherical shell of the table tennis ball is filled with a gas, and the pressure does not exceed 3 standard atmospheric pressures.  The table tennis according to any one of claims 1 to 4, characterized in that the spherical shell of the table tennis has a substantially uniform wall thickness, and the wall thickness of the spherical shell has an error of 0.04 mm or less.  The method for manufacturing a table tennis according to any one of claims 1 to 6, wherein the method comprises the following steps: adding raw materials for making table tennis to a spherical mold conforming to the size of the table tennis and closing the mold, The spherical mold is disposed in the rotational molding device such that the axes of the two rotating shafts of the rotational molding device pass through the center of the spherical cavity of the mold, and the axes of the two rotating shafts are perpendicular to each other; The two rotating shafts rotate and control the rotation speed in the range of 20 rpm to 3000 rpm, so that the raw material flowing in the mold can be uniformly attached to the inner wall of the cavity of the mold under the centrifugal force and its own gravity. The spherical mold is maintained in a rotating state, and after the raw material is solidified, it becomes a spherical shell, the mold is opened, and the spherical shell is taken out.  8. The manufacturing method according to claim 7, further comprising performing a surface treatment on the demolded spherical shell.  9. The manufacturing method according to claim 7, wherein after the mold is closed, the mold is filled with a gas of a certain pressure so that the spherical shell after the demolding has a pressure of not more than 3 standard atmospheric pressures.