{"id":18968,"date":"2026-10-18T11:06:13","date_gmt":"2026-10-18T03:06:13","guid":{"rendered":"https:\/\/hanchang.com.tw\/?p=18968"},"modified":"2026-10-18T11:06:13","modified_gmt":"2026-10-18T03:06:13","slug":"melamine-tableware-cracking-demolding-cooling-cure-en","status":"publish","type":"post","link":"https:\/\/hanchang.com.tw\/en\/melamine-tableware-cracking-demolding-cooling-cure-en\/","title":{"rendered":"Why Does Melamine Tableware Crack After Molding? Separate Demolding Stress, Cooling and Cure Shrinkage"},"content":{"rendered":"

Melamine tableware cracking should not be treated by automatically raising pressure or extending cure time. Record when the crack first becomes visible and where it starts; that separates demolding stress, cooling shrinkage, tool-temperature variation and the cure window.<\/strong> A crack that starts from a deep wall, sharp transition, rim or fixed ejection point while the mold opens deserves a tooling and release-path investigation. A part that looks intact at removal but cracks during cooling points the investigation toward temperature distribution, section changes, cure state and support after demolding.<\/p>\n

For a new production project, a single-color melamine tableware moulding machine<\/a> should be selected together with mold depth, wall transitions, removal space and the cooling workflow\u2014not by tonnage alone. Once each Han Chang melamine program is started, the press closes, applies pressure, degasses, forms the part and opens automatically. Operators load the compound, add a decal when the product requires one, add the necessary glazing powder, and remove the part. These separate stages make it practical to identify when a crack appears, but press control cannot compensate for an undercut, unsuitable compound or an unverified mold design.<\/p>\n

Start with the first appearance of the crack<\/h2>\n
\n\n\n\n\n\n\n\n\n\n\n
First appearance or crack origin<\/th>\nCheck first<\/th>\nWhy it matters<\/th>\nDo not assume<\/th>\n<\/tr>\n<\/thead>\n
Crack begins at a deep wall, undercut, rim or sharp corner during opening or removal<\/td>\nDraft, undercuts, tool surface, opening rate and removal direction<\/td>\nGeometric restraint can concentrate removal load at the weakest section<\/td>\nTotal press force is too low<\/td>\n<\/tr>\n
Fine radial or local cracks form around an ejector point<\/td>\nEjector position, loaded area, synchronization, speed and nearby wall thickness<\/td>\nA small contact area can generate a high local stress<\/td>\nMore ejection force is the answer<\/td>\n<\/tr>\n
The part is intact at demolding but cracks while cooling<\/td>\nTool-temperature distribution, thick-to-thin transitions, cooling support, cure and shrinkage<\/td>\nDifferent sections can cool and contract at different rates<\/td>\nEvery cycle needs more cure time<\/td>\n<\/tr>\n
The same cavity and direction crack repeatedly<\/td>\nLocal wear, thermal contact, venting, charge position and flow path<\/td>\nA fixed pattern is more consistent with a local condition than a random batch issue<\/td>\nThe whole compound batch is defective<\/td>\n<\/tr>\n
The affected cavity changes with batch or operator<\/td>\nCompound storage, moisture or volatiles, charge weight, preheat and transfer consistency<\/td>\nA moving pattern calls for a material and operating-baseline check<\/td>\nOne cavity should be modified first<\/td>\n<\/tr>\n
Plain molding looks sound, but a crack is seen after decal or glazing<\/td>\nPhotos after every opening, handling, positioning before repressing and part condition<\/td>\nA later visible crack may be an earlier microcrack that grew during another handling or pressing stage<\/td>\nThe decal or glazing powder is automatically the cause<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

This is a triage table, not a visual-only diagnosis. When cracking appears together with sticking or torn edges, use the related guide to melamine mold sticking and release-agent diagnosis<\/a> and review tool surface, draft, charge and cure as one system.<\/p>\n

Why \u201cpress it longer\u201d can also be the wrong answer<\/h2>\n

Melamine-formaldehyde is a thermoset. Its network develops during curing, so both insufficient cure and excessive cure can be poor outcomes. An undercured part may be weak, sticky or easily damaged during removal. Excessive temperature or pressing time can drive further condensation and shrinkage, increasing the risk of distortion or surface cracking.<\/p>\n

A 2020 Polymers<\/em> study followed the cure phases of a solid melamine-formaldehyde prepolymer. It notes that temperatures or pressing times that are too high can produce over-curing, excessive shrinkage, warpage and surface cracks. The study is not a production recipe for dinnerware: its resin and laboratory heating profile must not be copied into a factory setting. Its useful conclusion is that MF cure has a material-specific window; \u201chotter and longer\u201d is not a universal quality rule.<\/p>\n

On the shop floor, hold the compound batch, charge weight, preheat and tool constant. Measure actual tool-face temperature, then compare the condition at mold opening, after removal and after defined cooling. Change one variable at a time. Otherwise, a change in flow, venting, cure and release load can overlap and produce a misleading improvement.<\/p>\n

Demolding cracks require a geometry-and-load check<\/h2>\n

General thermoset compression-molding guides place crazing and cracking alongside back draft or undercuts, sharp thick-to-thin transitions, ejection rate, charge placement and controlled cooling. Those guides mainly cover BMC and related thermosets, not a fixed melamine dinnerware formulation. The diagnostic logic is still valuable: the crack origin shows where stress was concentrated.<\/p>\n

    \n
  1. Mark the origin, not only the finished fracture.<\/strong> Record cavity number, operator side, upper or lower mold, rim, deep wall, base, rib and parting line.<\/li>\n
  2. Record the first stage at which the crack is visible.<\/strong> Photograph the part after plain molding, manual removal, decal pressing when used, glazing, a defined cooling interval and stacking.<\/li>\n
  3. Review the release path.<\/strong> A white drag mark or scratch that precedes a crack on the same deep wall points toward surface, draft, undercut or removal direction before total machine force.<\/li>\n
  4. Review section transitions.<\/strong> Rims, feet, ribs and thick bases can create local differences in cooling and stiffness. A sharp transition deserves tooling review.<\/li>\n
  5. Standardize cooling support.<\/strong> Compare parts on the same surface, in the same orientation and after the same waiting time. Do not classify a handling or support change as a press-pressure problem.<\/li>\n<\/ol>\n

    Compound storage, preheating and charge placement also matter<\/h2>\n

    A melamine molding-compound supplier warns that moisture, contamination, damaged packaging and high storage temperature affect flow and moldability. It also states that preheating and molding conditions vary with product shape, thickness and the customer’s pressing conditions. When cracks suddenly move between cavities or follow a new batch, compare the lot, time since opening, storage environment, preheated condition, charge weight and charge placement before changing the mold.<\/p>\n

    Charge placement is important because it changes the flow pattern. If flow fronts repeatedly meet at a weak section, local joining and shrinkage may differ. Moving the charge is not a guaranteed correction; it is a controlled trial that should be evaluated while all other conditions remain fixed.<\/p>\n

    What the Han Chang melamine molding machine contributes<\/h2>\n

    Han Chang melamine presses provide an automatic cycle and adjustable degassing capability up to 99 settings. This is process flexibility, not a recommendation to use 99 degassing actions on every cycle, and not proof that every crack is caused by trapped gas. For single-color tableware, plain molding, optional decal pressing and the required glazing-powder stage are separate programs. After the operator starts a stage, the machine completes closing, pressure, degassing, forming and opening; loading, decoration, glazing and removal still involve the operator.<\/p>\n

    The practical value is repeatability:<\/p>\n