In the casting process, the ‘pattern’ is the replica of the intended object (such as a machine part or metal wheel). Patterns used in casting may be made of wood, metal or plastic. To produce a quality casting, it is essential that the pattern is carefully designed and constructed. Because the pattern determines the exact casting form, a casting can be no better than the pattern from which it was made. At Richmond Industries, we can either create a new pattern for you, or alter an existing one to fit your needs.
The main function of a pattern is to:
- Shape the mold cavity
- Provide accurate dimensions
- Provide a means of delivering liquid metal into the mold (this is the gating system)
A single piece pattern, or loose pattern, is the simplest. It is a replica of the item desired, usually in a slightly larger size to compensate for shrinkage. Gated patterns connect a number of loose pattern together with a series of runners that assist the alloy pour and are detached after the item is shaken from the original pattern. Segmented or multi-piece patterns create a casting in several pieces that are then joined in post-processing.
Match plate patterns are one where the top and bottom parts, known as the cope and drag positions, are mounted on opposite sides of the board. This allows for the patterns to be quickly pressed into the molding material. This type is used for larger castings.
Sweep patterns are used for symmetric molds and castings, which are counter strikes shapes rotated around a center axis or pole snooker thorough the molding material. A sweep pattern is a form of skeleton pattern such as a geometrical pattern that creates a mold by being moved through the molding material.
All patterns need to be constructed with allowances for any dimensional or structural changes which might happen during the casting process, such as an allowance for shrinkage when the alloy metal cools. The amount of shrinkage depends on the type of metal and on the sand casting process used.
Our complete pattern shop has the capabilities to mount patterns as well as add markings or modify runners, gating and risers to adjust for production anomalies, such as shrinkage or distortions as the metal cools. This inhouse capability means that we can provide quick turnaround of any adjustments needed to achieve client timelines.
Having control of the pattern making process means that we have complete quality control and the ability to alter and adjust as needed to accommodate changes in conditions. Our professional are always glad to sit down with our clients and determine what patterns are needed or if an existing pattern can be altered to fit the current needs.